This invention relates to the preparation of barium borate of a fixed barium to boron ratio for use in ceramic dielectric compositions, and more particularly to such a barium borate for use as a flux in barium titanate dielectric compositions for ceramic capacitors.
Barium borate (BaB.sub.2 O.sub.4) is used in some barium titanate ceramic formulations as a flux so as to lower the sintering temperature and maximize the density of the ceramic. BaB.sub.2 O.sub.4 is usually added in amounts of approximately 2% of the total ceramic composition. The effectiveness of BaB.sub.2 O.sub.4 as a flux is strongly dependent on the barium to boron ratio. Only with strict control of this ratio can reliably reproducible results be guaranteed.
Barium borate has been prepared in the prior art: by the solid state reaction of boric acid with either barium nitrate or barium carbonate; by the reaction of boric acid with barium chloride; by the simultaneous hydrolysis of barium and boron alkoxides; and, by the reaction of barium chloride with borox. None of these prior art preparative procedures guarantees stoichiometry control and none assures that the product will be uniquely BaB.sub.2 O.sub.4, with a Ba to B ratio of 1:2.
Attempts to control the barium to boron ratio of barium borate to 1:2 by pyrolyzing crystalline organic precursors have not been successful. Boric acid is known to form coordination compounds from appropriately substituted diols and hydroxy substituted diols and hydroxy substituted carboxylic acids. However, recrystallization and pyrolytic decomposition of several of the more promising organic compounds (viz: barium boro-di-salicylate; barium-boro-di-O,O'-biphenolate trihydrate; barium boro-tri-2,3-naphathalenediolate trihydrate; barium boro-di-pyrocatecholate trihydrate) failed to provide BaB.sub.2 O.sub.4. In all four cases the product obtained was contaminated by the presence of trace amounts of Ba.sub.2 B.sub.2 O.sub.2, in which the Ba to B ratio is 1:1 rather than 1:2, probably due to volatilization of some boron as an organo-boron compound during the pyrolysis. In addition the pyrolysis always left some residue of unoxidized carbon in the product.